The goals of this research are to advance our understanding of certain aspects of the language deficits in autism and to investigate their relationship to social-cognitive impairments that are at the core of this syndrome. Recently, a new hypothesis has been advanced which suggests that autism involves specific impairments in the acquisition of a 'theory of mind' which refers to the ability to understand mental states. Thus far, research on this hypothesis has focused primarily on autistic children's impaired conceptual understanding, however little work has been to investigate the relationship between such conceptual deficits and the primary language and communicative impairments which mark the autistic syndrome. There is also little work that directly addresses autistic children's ability to talk about mental states or to understand the meanings of mental state terms. Four studies are outlined here to address these issues. In each study high-functioning autistic subjects will be compared to language-- matched mentally retarded and normal controls. The first study investigates autistic children's understanding of false belief, a hallmark test of a theory of mind, to test whether previous findings may result from confounding linguistic factors. The second study examines autistic children's comprehension of pragmatic and semantic aspect of cognitive verbs which will be related to their use in spontaneous speech, and performance on false belief tasks. The third study will investigate what kinds of mental state language autistic children use to describe and explain human behavior. The final study will explore autistic children's narratives for fictional stories that require different sorts of psychological reasoning. Together, these studies will provide us with a clearer picture of the underlying language and social-cognitive deficits in autism, that may help us devise new assessment and intervention techniques.